The goals of this project center on characterization of the development of spatial vision in macaque monkeys. These monkeys form an animal model that can be used for testing hypotheses about the neural basis for the development of vision and its disruption by amblyopia, which is generally defined as a loss of vision due to abnormal visual conditions during development. We have been studying visual development in normal infant monkeys and in monkeys that have experimentally induced amblyopia in order to evaluate theories about the neural limitations on development and the disruption caused by amblyopia. We previously analyzed the performance of strabismic and anisometropic monkeys on various spatial tasks to establish the extent to which their deficits were related to the pattern of contrast sensitivity losses. We have found that in most cases, the pattern of contrast sensitivity loss can account for the loss of spatial precision in amblyopes, and that the pattern of deficits suggests a cortical substrate. We have recorded electrophysiological properties of neurons in primary visual cortex (V1) of amblyopic monkeys, to try to identify the neural basis for the amblyopic deficits. We have found a different pattern of results from strabismic and anisometropic monkeys. The strabismic monkeys have fairly balanced representation of the two eyes in V1 whereas the anisometropic monkeys have a distinct bias against the amblyopic eye. For both groups, the spatial and contrast response properties of the neurons driven by the amblyopic eyes were poor compared with those driven by the non-amblyopic eye.